tcp: add accessors to read/set tp->snd_cwnd

We had various bugs over the years with code
breaking the assumption that tp->snd_cwnd is greater
than zero.

Lately, syzbot reported the WARN_ON_ONCE(!tp->prior_cwnd) added
in commit 8b8a321ff72c ("tcp: fix zero cwnd in tcp_cwnd_reduction")
can trigger, and without a repro we would have to spend
considerable time finding the bug.

Instead of complaining too late, we want to catch where
and when tp->snd_cwnd is set to an illegal value.

Signed-off-by: Eric Dumazet <[e-mail]>
Suggested-by: Yuchung Cheng <[e-mail]>
Cc: Neal Cardwell <[e-mail]>
Acked-by: Yuchung Cheng <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

include/net/tcp.h

···
 
 #define TCP_INFINITE_SSTHRESH	0x7fffffff
 
+static inline u32 tcp_snd_cwnd(const struct tcp_sock *tp)
+{
+	return tp->snd_cwnd;
+}
+
+static inline void tcp_snd_cwnd_set(struct tcp_sock *tp, u32 val)
+{
+	WARN_ON_ONCE((int)val <= 0);
+	tp->snd_cwnd = val;
+}
+
 static inline bool tcp_in_slow_start(const struct tcp_sock *tp)
 {
-	return tp->snd_cwnd < tp->snd_ssthresh;
+	return tcp_snd_cwnd(tp) < tp->snd_ssthresh;
 }
 
 static inline bool tcp_in_initial_slowstart(const struct tcp_sock *tp)
···
 		return tp->snd_ssthresh;
 	else
 		return max(tp->snd_ssthresh,
-			   ((tp->snd_cwnd >> 1) +
-			    (tp->snd_cwnd >> 2)));
+			   ((tcp_snd_cwnd(tp) >> 1) +
+			    (tcp_snd_cwnd(tp) >> 2)));
 }
 
 /* Use define here intentionally to get WARN_ON location shown at the caller */
···
 
 	/* If in slow start, ensure cwnd grows to twice what was ACKed. */
 	if (tcp_in_slow_start(tp))
-		return tp->snd_cwnd < 2 * tp->max_packets_out;
+		return tcp_snd_cwnd(tp) < 2 * tp->max_packets_out;
 
 	return tp->is_cwnd_limited;
 }

include/trace/events/tcp.h

···
 		__entry->data_len = skb->len - __tcp_hdrlen(th);
 		__entry->snd_nxt = tp->snd_nxt;
 		__entry->snd_una = tp->snd_una;
-		__entry->snd_cwnd = tp->snd_cwnd;
+		__entry->snd_cwnd = tcp_snd_cwnd(tp);
 		__entry->snd_wnd = tp->snd_wnd;
 		__entry->rcv_wnd = tp->rcv_wnd;
 		__entry->ssthresh = tcp_current_ssthresh(sk);

net/core/filter.c

···
 				if (val <= 0 || tp->data_segs_out > tp->syn_data)
 					ret = -EINVAL;
 				else
-					tp->snd_cwnd = val;
+					tcp_snd_cwnd_set(tp, val);
 				break;
 			case TCP_BPF_SNDCWND_CLAMP:
 				if (val <= 0) {

net/ipv4/tcp.c

···
 	 * algorithms that we must have the following bandaid to talk
 	 * efficiently to them.  -DaveM
 	 */
-	tp->snd_cwnd = TCP_INIT_CWND;
+	tcp_snd_cwnd_set(tp, TCP_INIT_CWND);
 
 	/* There's a bubble in the pipe until at least the first ACK. */
 	tp->app_limited = ~0U;
···
 	icsk->icsk_rto_min = TCP_RTO_MIN;
 	icsk->icsk_delack_max = TCP_DELACK_MAX;
 	tp->snd_ssthresh = TCP_INFINITE_SSTHRESH;
-	tp->snd_cwnd = TCP_INIT_CWND;
+	tcp_snd_cwnd_set(tp, TCP_INIT_CWND);
 	tp->snd_cwnd_cnt = 0;
 	tp->window_clamp = 0;
 	tp->delivered = 0;
···
 	info->tcpi_max_pacing_rate = rate64;
 
 	info->tcpi_reordering = tp->reordering;
-	info->tcpi_snd_cwnd = tp->snd_cwnd;
+	info->tcpi_snd_cwnd = tcp_snd_cwnd(tp);
 
 	if (info->tcpi_state == TCP_LISTEN) {
 		/* listeners aliased fields :
···
 	rate64 = tcp_compute_delivery_rate(tp);
 	nla_put_u64_64bit(stats, TCP_NLA_DELIVERY_RATE, rate64, TCP_NLA_PAD);
 
-	nla_put_u32(stats, TCP_NLA_SND_CWND, tp->snd_cwnd);
+	nla_put_u32(stats, TCP_NLA_SND_CWND, tcp_snd_cwnd(tp));
 	nla_put_u32(stats, TCP_NLA_REORDERING, tp->reordering);
 	nla_put_u32(stats, TCP_NLA_MIN_RTT, tcp_min_rtt(tp));
 

net/ipv4/tcp_bbr.c

···
 	} else {			 /* no RTT sample yet */
 		rtt_us = USEC_PER_MSEC;	 /* use nominal default RTT */
 	}
-	bw = (u64)tp->snd_cwnd * BW_UNIT;
+	bw = (u64)tcp_snd_cwnd(tp) * BW_UNIT;
 	do_div(bw, rtt_us);
 	sk->sk_pacing_rate = bbr_bw_to_pacing_rate(sk, bw, bbr_high_gain);
 }
···
 	struct bbr *bbr = inet_csk_ca(sk);
 
 	if (bbr->prev_ca_state < TCP_CA_Recovery && bbr->mode != BBR_PROBE_RTT)
-		bbr->prior_cwnd = tp->snd_cwnd;  /* this cwnd is good enough */
+		bbr->prior_cwnd = tcp_snd_cwnd(tp);  /* this cwnd is good enough */
 	else  /* loss recovery or BBR_PROBE_RTT have temporarily cut cwnd */
-		bbr->prior_cwnd = max(bbr->prior_cwnd, tp->snd_cwnd);
+		bbr->prior_cwnd = max(bbr->prior_cwnd, tcp_snd_cwnd(tp));
 }
 
 static void bbr_cwnd_event(struct sock *sk, enum tcp_ca_event event)
···
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct bbr *bbr = inet_csk_ca(sk);
 	u8 prev_state = bbr->prev_ca_state, state = inet_csk(sk)->icsk_ca_state;
-	u32 cwnd = tp->snd_cwnd;
+	u32 cwnd = tcp_snd_cwnd(tp);
 
 	/* An ACK for P pkts should release at most 2*P packets. We do this
 	 * in two steps. First, here we deduct the number of lost packets.
···
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct bbr *bbr = inet_csk_ca(sk);
-	u32 cwnd = tp->snd_cwnd, target_cwnd = 0;
+	u32 cwnd = tcp_snd_cwnd(tp), target_cwnd = 0;
 
 	if (!acked)
 		goto done;  /* no packet fully ACKed; just apply caps */
···
 	cwnd = max(cwnd, bbr_cwnd_min_target);
 
 done:
-	tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);	/* apply global cap */
+	tcp_snd_cwnd_set(tp, min(cwnd, tp->snd_cwnd_clamp));	/* apply global cap */
 	if (bbr->mode == BBR_PROBE_RTT)  /* drain queue, refresh min_rtt */
-		tp->snd_cwnd = min(tp->snd_cwnd, bbr_cwnd_min_target);
+		tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), bbr_cwnd_min_target));
 }
 
 /* End cycle phase if it's time and/or we hit the phase's in-flight target. */
···
 	bbr->ack_epoch_acked = min_t(u32, 0xFFFFF,
 				     bbr->ack_epoch_acked + rs->acked_sacked);
 	extra_acked = bbr->ack_epoch_acked - expected_acked;
-	extra_acked = min(extra_acked, tp->snd_cwnd);
+	extra_acked = min(extra_acked, tcp_snd_cwnd(tp));
 	if (extra_acked > bbr->extra_acked[bbr->extra_acked_win_idx])
 		bbr->extra_acked[bbr->extra_acked_win_idx] = extra_acked;
 }
···
 		return;
 
 	bbr->min_rtt_stamp = tcp_jiffies32;  /* wait a while until PROBE_RTT */
-	tp->snd_cwnd = max(tp->snd_cwnd, bbr->prior_cwnd);
+	tcp_snd_cwnd_set(tp, max(tcp_snd_cwnd(tp), bbr->prior_cwnd));
 	bbr_reset_mode(sk);
 }
 
···
 	bbr->full_bw = 0;   /* spurious slow-down; reset full pipe detection */
 	bbr->full_bw_cnt = 0;
 	bbr_reset_lt_bw_sampling(sk);
-	return tcp_sk(sk)->snd_cwnd;
+	return tcp_snd_cwnd(tcp_sk(sk));
 }
 
 /* Entering loss recovery, so save cwnd for when we exit or undo recovery. */

net/ipv4/tcp_bic.c

···
 		if (!acked)
 			return;
 	}
-	bictcp_update(ca, tp->snd_cwnd);
+	bictcp_update(ca, tcp_snd_cwnd(tp));
 	tcp_cong_avoid_ai(tp, ca->cnt, acked);
 }
 
···
 	ca->epoch_start = 0;	/* end of epoch */
 
 	/* Wmax and fast convergence */
-	if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
-		ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
+	if (tcp_snd_cwnd(tp) < ca->last_max_cwnd && fast_convergence)
+		ca->last_max_cwnd = (tcp_snd_cwnd(tp) * (BICTCP_BETA_SCALE + beta))
 			/ (2 * BICTCP_BETA_SCALE);
 	else
-		ca->last_max_cwnd = tp->snd_cwnd;
+		ca->last_max_cwnd = tcp_snd_cwnd(tp);
 
-	if (tp->snd_cwnd <= low_window)
-		return max(tp->snd_cwnd >> 1U, 2U);
+	if (tcp_snd_cwnd(tp) <= low_window)
+		return max(tcp_snd_cwnd(tp) >> 1U, 2U);
 	else
-		return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
+		return max((tcp_snd_cwnd(tp) * beta) / BICTCP_BETA_SCALE, 2U);
 }
 
 static void bictcp_state(struct sock *sk, u8 new_state)

net/ipv4/tcp_cdg.c

···
 					      LINUX_MIB_TCPHYSTARTTRAINDETECT);
 				NET_ADD_STATS(sock_net(sk),
 					      LINUX_MIB_TCPHYSTARTTRAINCWND,
-					      tp->snd_cwnd);
-				tp->snd_ssthresh = tp->snd_cwnd;
+					      tcp_snd_cwnd(tp));
+				tp->snd_ssthresh = tcp_snd_cwnd(tp);
 				return;
 			}
 		}
···
 					      LINUX_MIB_TCPHYSTARTDELAYDETECT);
 				NET_ADD_STATS(sock_net(sk),
 					      LINUX_MIB_TCPHYSTARTDELAYCWND,
-					      tp->snd_cwnd);
-				tp->snd_ssthresh = tp->snd_cwnd;
+					      tcp_snd_cwnd(tp));
+				tp->snd_ssthresh = tcp_snd_cwnd(tp);
 			}
 		}
 	}
···
 			return false;
 	}
 
-	ca->shadow_wnd = max(ca->shadow_wnd, tp->snd_cwnd);
+	ca->shadow_wnd = max(ca->shadow_wnd, tcp_snd_cwnd(tp));
 	ca->state = CDG_BACKOFF;
 	tcp_enter_cwr(sk);
 	return true;
···
 	}
 
 	if (!tcp_is_cwnd_limited(sk)) {
-		ca->shadow_wnd = min(ca->shadow_wnd, tp->snd_cwnd);
+		ca->shadow_wnd = min(ca->shadow_wnd, tcp_snd_cwnd(tp));
 		return;
 	}
 
-	prior_snd_cwnd = tp->snd_cwnd;
+	prior_snd_cwnd = tcp_snd_cwnd(tp);
 	tcp_reno_cong_avoid(sk, ack, acked);
 
-	incr = tp->snd_cwnd - prior_snd_cwnd;
+	incr = tcp_snd_cwnd(tp) - prior_snd_cwnd;
 	ca->shadow_wnd = max(ca->shadow_wnd, ca->shadow_wnd + incr);
 }
 
···
 	struct tcp_sock *tp = tcp_sk(sk);
 
 	if (ca->state == CDG_BACKOFF)
-		return max(2U, (tp->snd_cwnd * min(1024U, backoff_beta)) >> 10);
+		return max(2U, (tcp_snd_cwnd(tp) * min(1024U, backoff_beta)) >> 10);
 
 	if (ca->state == CDG_NONFULL && use_tolerance)
-		return tp->snd_cwnd;
+		return tcp_snd_cwnd(tp);
 
-	ca->shadow_wnd = min(ca->shadow_wnd >> 1, tp->snd_cwnd);
+	ca->shadow_wnd = min(ca->shadow_wnd >> 1, tcp_snd_cwnd(tp));
 	if (use_shadow)
-		return max3(2U, ca->shadow_wnd, tp->snd_cwnd >> 1);
-	return max(2U, tp->snd_cwnd >> 1);
+		return max3(2U, ca->shadow_wnd, tcp_snd_cwnd(tp) >> 1);
+	return max(2U, tcp_snd_cwnd(tp) >> 1);
 }
 
 static void tcp_cdg_cwnd_event(struct sock *sk, const enum tcp_ca_event ev)
···
 
 		ca->gradients = gradients;
 		ca->rtt_seq = tp->snd_nxt;
-		ca->shadow_wnd = tp->snd_cwnd;
+		ca->shadow_wnd = tcp_snd_cwnd(tp);
 		break;
 	case CA_EVENT_COMPLETE_CWR:
 		ca->state = CDG_UNKNOWN;
···
 		ca->gradients = kcalloc(window, sizeof(ca->gradients[0]),
 					GFP_NOWAIT | __GFP_NOWARN);
 	ca->rtt_seq = tp->snd_nxt;
-	ca->shadow_wnd = tp->snd_cwnd;
+	ca->shadow_wnd = tcp_snd_cwnd(tp);
 }
 
 static void tcp_cdg_release(struct sock *sk)

net/ipv4/tcp_cong.c

···
  */
 u32 tcp_slow_start(struct tcp_sock *tp, u32 acked)
 {
-	u32 cwnd = min(tp->snd_cwnd + acked, tp->snd_ssthresh);
+	u32 cwnd = min(tcp_snd_cwnd(tp) + acked, tp->snd_ssthresh);
 
-	acked -= cwnd - tp->snd_cwnd;
-	tp->snd_cwnd = min(cwnd, tp->snd_cwnd_clamp);
+	acked -= cwnd - tcp_snd_cwnd(tp);
+	tcp_snd_cwnd_set(tp, min(cwnd, tp->snd_cwnd_clamp));
 
 	return acked;
 }
···
 	/* If credits accumulated at a higher w, apply them gently now. */
 	if (tp->snd_cwnd_cnt >= w) {
 		tp->snd_cwnd_cnt = 0;
-		tp->snd_cwnd++;
+		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
 	}
 
 	tp->snd_cwnd_cnt += acked;
···
 		u32 delta = tp->snd_cwnd_cnt / w;
 
 		tp->snd_cwnd_cnt -= delta * w;
-		tp->snd_cwnd += delta;
+		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + delta);
 	}
-	tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_cwnd_clamp);
+	tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), tp->snd_cwnd_clamp));
 }
 EXPORT_SYMBOL_GPL(tcp_cong_avoid_ai);
 
···
 			return;
 	}
 	/* In dangerous area, increase slowly. */
-	tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
+	tcp_cong_avoid_ai(tp, tcp_snd_cwnd(tp), acked);
 }
 EXPORT_SYMBOL_GPL(tcp_reno_cong_avoid);
 
···
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 
-	return max(tp->snd_cwnd >> 1U, 2U);
+	return max(tcp_snd_cwnd(tp) >> 1U, 2U);
 }
 EXPORT_SYMBOL_GPL(tcp_reno_ssthresh);
 
···
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 
-	return max(tp->snd_cwnd, tp->prior_cwnd);
+	return max(tcp_snd_cwnd(tp), tp->prior_cwnd);
 }
 EXPORT_SYMBOL_GPL(tcp_reno_undo_cwnd);
 

net/ipv4/tcp_cubic.c

···
 		if (!acked)
 			return;
 	}
-	bictcp_update(ca, tp->snd_cwnd, acked);
+	bictcp_update(ca, tcp_snd_cwnd(tp), acked);
 	tcp_cong_avoid_ai(tp, ca->cnt, acked);
 }
 
···
 	ca->epoch_start = 0;	/* end of epoch */
 
 	/* Wmax and fast convergence */
-	if (tp->snd_cwnd < ca->last_max_cwnd && fast_convergence)
-		ca->last_max_cwnd = (tp->snd_cwnd * (BICTCP_BETA_SCALE + beta))
+	if (tcp_snd_cwnd(tp) < ca->last_max_cwnd && fast_convergence)
+		ca->last_max_cwnd = (tcp_snd_cwnd(tp) * (BICTCP_BETA_SCALE + beta))
 			/ (2 * BICTCP_BETA_SCALE);
 	else
-		ca->last_max_cwnd = tp->snd_cwnd;
+		ca->last_max_cwnd = tcp_snd_cwnd(tp);
 
-	return max((tp->snd_cwnd * beta) / BICTCP_BETA_SCALE, 2U);
+	return max((tcp_snd_cwnd(tp) * beta) / BICTCP_BETA_SCALE, 2U);
 }
 
 static void cubictcp_state(struct sock *sk, u8 new_state)
···
 				ca->found = 1;
 				pr_debug("hystart_ack_train (%u > %u) delay_min %u (+ ack_delay %u) cwnd %u\n",
 					 now - ca->round_start, threshold,
-					 ca->delay_min, hystart_ack_delay(sk), tp->snd_cwnd);
+					 ca->delay_min, hystart_ack_delay(sk), tcp_snd_cwnd(tp));
 				NET_INC_STATS(sock_net(sk),
 					      LINUX_MIB_TCPHYSTARTTRAINDETECT);
 				NET_ADD_STATS(sock_net(sk),
 					      LINUX_MIB_TCPHYSTARTTRAINCWND,
-					      tp->snd_cwnd);
-				tp->snd_ssthresh = tp->snd_cwnd;
+					      tcp_snd_cwnd(tp));
+				tp->snd_ssthresh = tcp_snd_cwnd(tp);
 			}
 		}
 	}
···
 					      LINUX_MIB_TCPHYSTARTDELAYDETECT);
 				NET_ADD_STATS(sock_net(sk),
 					      LINUX_MIB_TCPHYSTARTDELAYCWND,
-					      tp->snd_cwnd);
-				tp->snd_ssthresh = tp->snd_cwnd;
+					      tcp_snd_cwnd(tp));
+				tp->snd_ssthresh = tcp_snd_cwnd(tp);
 			}
 		}
 	}
···
 
 	/* hystart triggers when cwnd is larger than some threshold */
 	if (!ca->found && tcp_in_slow_start(tp) && hystart &&
-	    tp->snd_cwnd >= hystart_low_window)
+	    tcp_snd_cwnd(tp) >= hystart_low_window)
 		hystart_update(sk, delay);
 }
 

net/ipv4/tcp_dctcp.c

···
 	struct dctcp *ca = inet_csk_ca(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	ca->loss_cwnd = tp->snd_cwnd;
-	return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->dctcp_alpha) >> 11U), 2U);
+	ca->loss_cwnd = tcp_snd_cwnd(tp);
+	return max(tcp_snd_cwnd(tp) - ((tcp_snd_cwnd(tp) * ca->dctcp_alpha) >> 11U), 2U);
 }
 
 static void dctcp_update_alpha(struct sock *sk, u32 flags)
···
 	struct dctcp *ca = inet_csk_ca(sk);
 	struct tcp_sock *tp = tcp_sk(sk);
 
-	ca->loss_cwnd = tp->snd_cwnd;
-	tp->snd_ssthresh = max(tp->snd_cwnd >> 1U, 2U);
+	ca->loss_cwnd = tcp_snd_cwnd(tp);
+	tp->snd_ssthresh = max(tcp_snd_cwnd(tp) >> 1U, 2U);
 }
 
 static void dctcp_state(struct sock *sk, u8 new_state)
···
 static u32 dctcp_cwnd_undo(struct sock *sk)
 {
 	const struct dctcp *ca = inet_csk_ca(sk);
+	struct tcp_sock *tp = tcp_sk(sk);
 
-	return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
+	return max(tcp_snd_cwnd(tp), ca->loss_cwnd);
 }
 
 static struct tcp_congestion_ops dctcp __read_mostly = {

net/ipv4/tcp_highspeed.c

···
 		 *     snd_cwnd <=
 		 *     hstcp_aimd_vals[ca->ai].cwnd
 		 */
-		if (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd) {
-			while (tp->snd_cwnd > hstcp_aimd_vals[ca->ai].cwnd &&
+		if (tcp_snd_cwnd(tp) > hstcp_aimd_vals[ca->ai].cwnd) {
+			while (tcp_snd_cwnd(tp) > hstcp_aimd_vals[ca->ai].cwnd &&
 			       ca->ai < HSTCP_AIMD_MAX - 1)
 				ca->ai++;
-		} else if (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd) {
-			while (ca->ai && tp->snd_cwnd <= hstcp_aimd_vals[ca->ai-1].cwnd)
+		} else if (ca->ai && tcp_snd_cwnd(tp) <= hstcp_aimd_vals[ca->ai-1].cwnd) {
+			while (ca->ai && tcp_snd_cwnd(tp) <= hstcp_aimd_vals[ca->ai-1].cwnd)
 				ca->ai--;
 		}
 
 		/* Do additive increase */
-		if (tp->snd_cwnd < tp->snd_cwnd_clamp) {
+		if (tcp_snd_cwnd(tp) < tp->snd_cwnd_clamp) {
 			/* cwnd = cwnd + a(w) / cwnd */
 			tp->snd_cwnd_cnt += ca->ai + 1;
-			if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
-				tp->snd_cwnd_cnt -= tp->snd_cwnd;
-				tp->snd_cwnd++;
+			if (tp->snd_cwnd_cnt >= tcp_snd_cwnd(tp)) {
+				tp->snd_cwnd_cnt -= tcp_snd_cwnd(tp);
+				tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
 			}
 		}
 	}
···
 	struct hstcp *ca = inet_csk_ca(sk);
 
 	/* Do multiplicative decrease */
-	return max(tp->snd_cwnd - ((tp->snd_cwnd * hstcp_aimd_vals[ca->ai].md) >> 8), 2U);
+	return max(tcp_snd_cwnd(tp) - ((tcp_snd_cwnd(tp) * hstcp_aimd_vals[ca->ai].md) >> 8), 2U);
 }
 
 static struct tcp_congestion_ops tcp_highspeed __read_mostly = {

net/ipv4/tcp_htcp.c

···
 
 	ca->packetcount += sample->pkts_acked;
 
-	if (ca->packetcount >= tp->snd_cwnd - (ca->alpha >> 7 ? : 1) &&
+	if (ca->packetcount >= tcp_snd_cwnd(tp) - (ca->alpha >> 7 ? : 1) &&
 	    now - ca->lasttime >= ca->minRTT &&
 	    ca->minRTT > 0) {
 		__u32 cur_Bi = ca->packetcount * HZ / (now - ca->lasttime);
···
 	const struct htcp *ca = inet_csk_ca(sk);
 
 	htcp_param_update(sk);
-	return max((tp->snd_cwnd * ca->beta) >> 7, 2U);
+	return max((tcp_snd_cwnd(tp) * ca->beta) >> 7, 2U);
 }
 
 static void htcp_cong_avoid(struct sock *sk, u32 ack, u32 acked)
···
 		/* In dangerous area, increase slowly.
 		 * In theory this is tp->snd_cwnd += alpha / tp->snd_cwnd
 		 */
-		if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tp->snd_cwnd) {
-			if (tp->snd_cwnd < tp->snd_cwnd_clamp)
-				tp->snd_cwnd++;
+		if ((tp->snd_cwnd_cnt * ca->alpha)>>7 >= tcp_snd_cwnd(tp)) {
+			if (tcp_snd_cwnd(tp) < tp->snd_cwnd_clamp)
+				tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
 			tp->snd_cwnd_cnt = 0;
 			htcp_alpha_update(ca);
 		} else

net/ipv4/tcp_hybla.c

···
 	ca->rho2_7ls = 0;
 	ca->snd_cwnd_cents = 0;
 	ca->hybla_en = true;
-	tp->snd_cwnd = 2;
+	tcp_snd_cwnd_set(tp, 2);
 	tp->snd_cwnd_clamp = 65535;
 
 	/* 1st Rho measurement based on initial srtt */
···
 
 	/* set minimum rtt as this is the 1st ever seen */
 	ca->minrtt_us = tp->srtt_us;
-	tp->snd_cwnd = ca->rho;
+	tcp_snd_cwnd_set(tp, ca->rho);
 }
 
 static void hybla_state(struct sock *sk, u8 ca_state)
···
 		 * as long as increment is estimated as (rho<<7)/window
 		 * it already is <<7 and we can easily count its fractions.
 		 */
-		increment = ca->rho2_7ls / tp->snd_cwnd;
+		increment = ca->rho2_7ls / tcp_snd_cwnd(tp);
 		if (increment < 128)
 			tp->snd_cwnd_cnt++;
 	}
 
 	odd = increment % 128;
-	tp->snd_cwnd += increment >> 7;
+	tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + (increment >> 7));
 	ca->snd_cwnd_cents += odd;
 
 	/* check when fractions goes >=128 and increase cwnd by 1. */
 	while (ca->snd_cwnd_cents >= 128) {
-		tp->snd_cwnd++;
+		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
 		ca->snd_cwnd_cents -= 128;
 		tp->snd_cwnd_cnt = 0;
 	}
 	/* check when cwnd has not been incremented for a while */
-	if (increment == 0 && odd == 0 && tp->snd_cwnd_cnt >= tp->snd_cwnd) {
-		tp->snd_cwnd++;
+	if (increment == 0 && odd == 0 && tp->snd_cwnd_cnt >= tcp_snd_cwnd(tp)) {
+		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
 		tp->snd_cwnd_cnt = 0;
 	}
 	/* clamp down slowstart cwnd to ssthresh value. */
 	if (is_slowstart)
-		tp->snd_cwnd = min(tp->snd_cwnd, tp->snd_ssthresh);
+		tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), tp->snd_ssthresh));
 
-	tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);
+	tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp), tp->snd_cwnd_clamp));
 }
 
 static struct tcp_congestion_ops tcp_hybla __read_mostly = {

net/ipv4/tcp_illinois.c

···
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct illinois *ca = inet_csk_ca(sk);
 
-	if (tp->snd_cwnd < win_thresh) {
+	if (tcp_snd_cwnd(tp) < win_thresh) {
 		ca->alpha = ALPHA_BASE;
 		ca->beta = BETA_BASE;
 	} else if (ca->cnt_rtt > 0) {
···
 		 * tp->snd_cwnd += alpha/tp->snd_cwnd
 		*/
 		delta = (tp->snd_cwnd_cnt * ca->alpha) >> ALPHA_SHIFT;
-		if (delta >= tp->snd_cwnd) {
-			tp->snd_cwnd = min(tp->snd_cwnd + delta / tp->snd_cwnd,
-					   (u32)tp->snd_cwnd_clamp);
+		if (delta >= tcp_snd_cwnd(tp)) {
+			tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp) + delta / tcp_snd_cwnd(tp),
+						 (u32)tp->snd_cwnd_clamp));
 			tp->snd_cwnd_cnt = 0;
 		}
 	}
···
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct illinois *ca = inet_csk_ca(sk);
+	u32 decr;
 
 	/* Multiplicative decrease */
-	return max(tp->snd_cwnd - ((tp->snd_cwnd * ca->beta) >> BETA_SHIFT), 2U);
+	decr = (tcp_snd_cwnd(tp) * ca->beta) >> BETA_SHIFT;
+	return max(tcp_snd_cwnd(tp) - decr, 2U);
 }
 
 /* Extract info for Tcp socket info provided via netlink. */

net/ipv4/tcp_input.c

···
 	per_mss = roundup_pow_of_two(per_mss) +
 		  SKB_DATA_ALIGN(sizeof(struct sk_buff));
 
-	nr_segs = max_t(u32, TCP_INIT_CWND, tp->snd_cwnd);
+	nr_segs = max_t(u32, TCP_INIT_CWND, tcp_snd_cwnd(tp));
 	nr_segs = max_t(u32, nr_segs, tp->reordering + 1);
 
 	/* Fast Recovery (RFC 5681 3.2) :
···
 	 *	 If snd_cwnd >= (tp->snd_ssthresh / 2), we are approaching
 	 *	 end of slow start and should slow down.
 	 */
-	if (tp->snd_cwnd < tp->snd_ssthresh / 2)
+	if (tcp_snd_cwnd(tp) < tp->snd_ssthresh / 2)
 		rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ss_ratio;
 	else
 		rate *= sock_net(sk)->ipv4.sysctl_tcp_pacing_ca_ratio;
 
-	rate *= max(tp->snd_cwnd, tp->packets_out);
+	rate *= max(tcp_snd_cwnd(tp), tp->packets_out);
 
 	if (likely(tp->srtt_us))
 		do_div(rate, tp->srtt_us);
···
 	    !after(tp->high_seq, tp->snd_una) ||
 	    (icsk->icsk_ca_state == TCP_CA_Loss && !icsk->icsk_retransmits)) {
 		tp->prior_ssthresh = tcp_current_ssthresh(sk);
-		tp->prior_cwnd = tp->snd_cwnd;
+		tp->prior_cwnd = tcp_snd_cwnd(tp);
 		tp->snd_ssthresh = icsk->icsk_ca_ops->ssthresh(sk);
 		tcp_ca_event(sk, CA_EVENT_LOSS);
 		tcp_init_undo(tp);
 	}
-	tp->snd_cwnd	   = tcp_packets_in_flight(tp) + 1;
+	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + 1);
 	tp->snd_cwnd_cnt   = 0;
 	tp->snd_cwnd_stamp = tcp_jiffies32;
 
···
 		pr_debug("Undo %s %pI4/%u c%u l%u ss%u/%u p%u\n",
 			 msg,
 			 &inet->inet_daddr, ntohs(inet->inet_dport),
-			 tp->snd_cwnd, tcp_left_out(tp),
+			 tcp_snd_cwnd(tp), tcp_left_out(tp),
 			 tp->snd_ssthresh, tp->prior_ssthresh,
 			 tp->packets_out);
 	}
···
 		pr_debug("Undo %s %pI6/%u c%u l%u ss%u/%u p%u\n",
 			 msg,
 			 &sk->sk_v6_daddr, ntohs(inet->inet_dport),
-			 tp->snd_cwnd, tcp_left_out(tp),
+			 tcp_snd_cwnd(tp), tcp_left_out(tp),
 			 tp->snd_ssthresh, tp->prior_ssthresh,
 			 tp->packets_out);
 	}
···
 	if (tp->prior_ssthresh) {
 		const struct inet_connection_sock *icsk = inet_csk(sk);
 
-		tp->snd_cwnd = icsk->icsk_ca_ops->undo_cwnd(sk);
+		tcp_snd_cwnd_set(tp, icsk->icsk_ca_ops->undo_cwnd(sk));
 
 		if (tp->prior_ssthresh > tp->snd_ssthresh) {
 			tp->snd_ssthresh = tp->prior_ssthresh;
···
 	tp->high_seq = tp->snd_nxt;
 	tp->tlp_high_seq = 0;
 	tp->snd_cwnd_cnt = 0;
-	tp->prior_cwnd = tp->snd_cwnd;
+	tp->prior_cwnd = tcp_snd_cwnd(tp);
 	tp->prr_delivered = 0;
 	tp->prr_out = 0;
 	tp->snd_ssthresh = inet_csk(sk)->icsk_ca_ops->ssthresh(sk);
···
 	}
 	/* Force a fast retransmit upon entering fast recovery */
 	sndcnt = max(sndcnt, (tp->prr_out ? 0 : 1));
-	tp->snd_cwnd = tcp_packets_in_flight(tp) + sndcnt;
+	tcp_snd_cwnd_set(tp, tcp_packets_in_flight(tp) + sndcnt);
 }
 
 static inline void tcp_end_cwnd_reduction(struct sock *sk)
···
 	/* Reset cwnd to ssthresh in CWR or Recovery (unless it's undone) */
 	if (tp->snd_ssthresh < TCP_INFINITE_SSTHRESH &&
 	    (inet_csk(sk)->icsk_ca_state == TCP_CA_CWR || tp->undo_marker)) {
-		tp->snd_cwnd = tp->snd_ssthresh;
+		tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
 		tp->snd_cwnd_stamp = tcp_jiffies32;
 	}
 	tcp_ca_event(sk, CA_EVENT_COMPLETE_CWR);
···
 
 	/* FIXME: breaks with very large cwnd */
 	tp->prior_ssthresh = tcp_current_ssthresh(sk);
-	tp->snd_cwnd = tp->snd_cwnd *
-		       tcp_mss_to_mtu(sk, tp->mss_cache) /
-		       icsk->icsk_mtup.probe_size;
+	tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) *
+			     tcp_mss_to_mtu(sk, tp->mss_cache) /
+			     icsk->icsk_mtup.probe_size);
 	tp->snd_cwnd_cnt = 0;
 	tp->snd_cwnd_stamp = tcp_jiffies32;
 	tp->snd_ssthresh = tcp_current_ssthresh(sk);
···
 		    tp->snd_una == tp->mtu_probe.probe_seq_start) {
 			tcp_mtup_probe_failed(sk);
 			/* Restores the reduction we did in tcp_mtup_probe() */
-			tp->snd_cwnd++;
+			tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
 			tcp_simple_retransmit(sk);
 			return;
 		}
···
 		return false;
 
 	/* If we filled the congestion window, do not expand.  */
-	if (tcp_packets_in_flight(tp) >= tp->snd_cwnd)
+	if (tcp_packets_in_flight(tp) >= tcp_snd_cwnd(tp))
 		return false;
 
 	return true;
···
 	 * retransmission has occurred.
 	 */
 	if (tp->total_retrans > 1 && tp->undo_marker)
-		tp->snd_cwnd = 1;
+		tcp_snd_cwnd_set(tp, 1);
 	else
-		tp->snd_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
+		tcp_snd_cwnd_set(tp, tcp_init_cwnd(tp, __sk_dst_get(sk)));
 	tp->snd_cwnd_stamp = tcp_jiffies32;
 
 	bpf_skops_established(sk, bpf_op, skb);

net/ipv4/tcp_ipv4.c

···
 		jiffies_to_clock_t(icsk->icsk_rto),
 		jiffies_to_clock_t(icsk->icsk_ack.ato),
 		(icsk->icsk_ack.quick << 1) | inet_csk_in_pingpong_mode(sk),
-		tp->snd_cwnd,
+		tcp_snd_cwnd(tp),
 		state == TCP_LISTEN ?
 		    fastopenq->max_qlen :
 		    (tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh));

net/ipv4/tcp_lp.c

···
 		lp->flag &= ~LP_WITHIN_THR;
 
 	pr_debug("TCP-LP: %05o|%5u|%5u|%15u|%15u|%15u\n", lp->flag,
-		 tp->snd_cwnd, lp->remote_hz, lp->owd_min, lp->owd_max,
+		 tcp_snd_cwnd(tp), lp->remote_hz, lp->owd_min, lp->owd_max,
 		 lp->sowd >> 3);
 
 	if (lp->flag & LP_WITHIN_THR)
···
 	/* happened within inference
 	 * drop snd_cwnd into 1 */
 	if (lp->flag & LP_WITHIN_INF)
-		tp->snd_cwnd = 1U;
+		tcp_snd_cwnd_set(tp, 1U);
 
 	/* happened after inference
 	 * cut snd_cwnd into half */
 	else
-		tp->snd_cwnd = max(tp->snd_cwnd >> 1U, 1U);
+		tcp_snd_cwnd_set(tp, max(tcp_snd_cwnd(tp) >> 1U, 1U));
 
 	/* record this drop time */
 	lp->last_drop = now;

net/ipv4/tcp_metrics.c

···
 		if (!net->ipv4.sysctl_tcp_no_ssthresh_metrics_save &&
 		    !tcp_metric_locked(tm, TCP_METRIC_SSTHRESH)) {
 			val = tcp_metric_get(tm, TCP_METRIC_SSTHRESH);
-			if (val && (tp->snd_cwnd >> 1) > val)
+			if (val && (tcp_snd_cwnd(tp) >> 1) > val)
 				tcp_metric_set(tm, TCP_METRIC_SSTHRESH,
-					       tp->snd_cwnd >> 1);
+					       tcp_snd_cwnd(tp) >> 1);
 		}
 		if (!tcp_metric_locked(tm, TCP_METRIC_CWND)) {
 			val = tcp_metric_get(tm, TCP_METRIC_CWND);
-			if (tp->snd_cwnd > val)
+			if (tcp_snd_cwnd(tp) > val)
 				tcp_metric_set(tm, TCP_METRIC_CWND,
-					       tp->snd_cwnd);
+					       tcp_snd_cwnd(tp));
 		}
 	} else if (!tcp_in_slow_start(tp) &&
 		   icsk->icsk_ca_state == TCP_CA_Open) {
···
 		if (!net->ipv4.sysctl_tcp_no_ssthresh_metrics_save &&
 		    !tcp_metric_locked(tm, TCP_METRIC_SSTHRESH))
 			tcp_metric_set(tm, TCP_METRIC_SSTHRESH,
-				       max(tp->snd_cwnd >> 1, tp->snd_ssthresh));
+				       max(tcp_snd_cwnd(tp) >> 1, tp->snd_ssthresh));
 		if (!tcp_metric_locked(tm, TCP_METRIC_CWND)) {
 			val = tcp_metric_get(tm, TCP_METRIC_CWND);
-			tcp_metric_set(tm, TCP_METRIC_CWND, (val + tp->snd_cwnd) >> 1);
+			tcp_metric_set(tm, TCP_METRIC_CWND, (val + tcp_snd_cwnd(tp)) >> 1);
 		}
 	} else {
 		/* Else slow start did not finish, cwnd is non-sense,

net/ipv4/tcp_nv.c

···
 	}
 
 	if (ca->cwnd_growth_factor < 0) {
-		cnt = tp->snd_cwnd << -ca->cwnd_growth_factor;
+		cnt = tcp_snd_cwnd(tp) << -ca->cwnd_growth_factor;
 		tcp_cong_avoid_ai(tp, cnt, acked);
 	} else {
-		cnt = max(4U, tp->snd_cwnd >> ca->cwnd_growth_factor);
+		cnt = max(4U, tcp_snd_cwnd(tp) >> ca->cwnd_growth_factor);
 		tcp_cong_avoid_ai(tp, cnt, acked);
 	}
 }
···
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 
-	return max((tp->snd_cwnd * nv_loss_dec_factor) >> 10, 2U);
+	return max((tcp_snd_cwnd(tp) * nv_loss_dec_factor) >> 10, 2U);
 }
 
 static void tcpnv_state(struct sock *sk, u8 new_state)
···
 		return;
 
 	/* Stop cwnd growth if we were in catch up mode */
-	if (ca->nv_catchup && tp->snd_cwnd >= nv_min_cwnd) {
+	if (ca->nv_catchup && tcp_snd_cwnd(tp) >= nv_min_cwnd) {
 		ca->nv_catchup = 0;
 		ca->nv_allow_cwnd_growth = 0;
 	}
···
 		 * if cwnd < max_win, grow cwnd
 		 * else leave the same
 		 */
-		if (tp->snd_cwnd > max_win) {
+		if (tcp_snd_cwnd(tp) > max_win) {
 			/* there is congestion, check that it is ok
 			 * to make a CA decision
 			 * 1. We should have at least nv_dec_eval_min_calls
···
 			ca->nv_allow_cwnd_growth = 0;
 			tp->snd_ssthresh =
 				(nv_ssthresh_factor * max_win) >> 3;
-			if (tp->snd_cwnd - max_win > 2) {
+			if (tcp_snd_cwnd(tp) - max_win > 2) {
 				/* gap > 2, we do exponential cwnd decrease */
 				int dec;
 
-				dec = max(2U, ((tp->snd_cwnd - max_win) *
+				dec = max(2U, ((tcp_snd_cwnd(tp) - max_win) *
 					       nv_cong_dec_mult) >> 7);
-				tp->snd_cwnd -= dec;
+				tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) - dec);
 			} else if (nv_cong_dec_mult > 0) {
-				tp->snd_cwnd = max_win;
+				tcp_snd_cwnd_set(tp, max_win);
 			}
 			if (ca->cwnd_growth_factor > 0)
 				ca->cwnd_growth_factor = 0;
 			ca->nv_no_cong_cnt = 0;
-		} else if (tp->snd_cwnd <= max_win - nv_pad_buffer) {
+		} else if (tcp_snd_cwnd(tp) <= max_win - nv_pad_buffer) {
 			/* There is no congestion, grow cwnd if allowed*/
 			if (ca->nv_eval_call_cnt < nv_inc_eval_min_calls)
 				return;
···
 		 * (it wasn't before, if it is now is because nv
 		 *  decreased it).
 		 */
-		if (tp->snd_cwnd < nv_min_cwnd)
-			tp->snd_cwnd = nv_min_cwnd;
+		if (tcp_snd_cwnd(tp) < nv_min_cwnd)
+			tcp_snd_cwnd_set(tp, nv_min_cwnd);
 	}
 }
 

net/ipv4/tcp_output.c

···
 {
 	struct tcp_sock *tp = tcp_sk(sk);
 	u32 restart_cwnd = tcp_init_cwnd(tp, __sk_dst_get(sk));
-	u32 cwnd = tp->snd_cwnd;
+	u32 cwnd = tcp_snd_cwnd(tp);
 
 	tcp_ca_event(sk, CA_EVENT_CWND_RESTART);
 
···
 
 	while ((delta -= inet_csk(sk)->icsk_rto) > 0 && cwnd > restart_cwnd)
 		cwnd >>= 1;
-	tp->snd_cwnd = max(cwnd, restart_cwnd);
+	tcp_snd_cwnd_set(tp, max(cwnd, restart_cwnd));
 	tp->snd_cwnd_stamp = tcp_jiffies32;
 	tp->snd_cwnd_used = 0;
 }
···
 		struct tcp_sock *tp = tcp_sk(sk);
 
 		if (tp->lost_out > tp->retrans_out &&
-		    tp->snd_cwnd > tcp_packets_in_flight(tp)) {
+		    tcp_snd_cwnd(tp) > tcp_packets_in_flight(tp)) {
 			tcp_mstamp_refresh(tp);
 			tcp_xmit_retransmit_queue(sk);
 		}
···
 		/* Limited by application or receiver window. */
 		u32 init_win = tcp_init_cwnd(tp, __sk_dst_get(sk));
 		u32 win_used = max(tp->snd_cwnd_used, init_win);
-		if (win_used < tp->snd_cwnd) {
+		if (win_used < tcp_snd_cwnd(tp)) {
 			tp->snd_ssthresh = tcp_current_ssthresh(sk);
-			tp->snd_cwnd = (tp->snd_cwnd + win_used) >> 1;
+			tcp_snd_cwnd_set(tp, (tcp_snd_cwnd(tp) + win_used) >> 1);
 		}
 		tp->snd_cwnd_used = 0;
 	}
···
 		return 1;
 
 	in_flight = tcp_packets_in_flight(tp);
-	cwnd = tp->snd_cwnd;
+	cwnd = tcp_snd_cwnd(tp);
 	if (in_flight >= cwnd)
 		return 0;
 
···
 	in_flight = tcp_packets_in_flight(tp);
 
 	BUG_ON(tcp_skb_pcount(skb) <= 1);
-	BUG_ON(tp->snd_cwnd <= in_flight);
+	BUG_ON(tcp_snd_cwnd(tp) <= in_flight);
 
 	send_win = tcp_wnd_end(tp) - TCP_SKB_CB(skb)->seq;
 
 	/* From in_flight test above, we know that cwnd > in_flight.  */
-	cong_win = (tp->snd_cwnd - in_flight) * tp->mss_cache;
+	cong_win = (tcp_snd_cwnd(tp) - in_flight) * tp->mss_cache;
 
 	limit = min(send_win, cong_win);
 
···
 
 	win_divisor = READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_tso_win_divisor);
 	if (win_divisor) {
-		u32 chunk = min(tp->snd_wnd, tp->snd_cwnd * tp->mss_cache);
+		u32 chunk = min(tp->snd_wnd, tcp_snd_cwnd(tp) * tp->mss_cache);
 
 		/* If at least some fraction of a window is available,
 		 * just use it.
···
 	if (likely(!icsk->icsk_mtup.enabled ||
 		   icsk->icsk_mtup.probe_size ||
 		   inet_csk(sk)->icsk_ca_state != TCP_CA_Open ||
-		   tp->snd_cwnd < 11 ||
+		   tcp_snd_cwnd(tp) < 11 ||
 		   tp->rx_opt.num_sacks || tp->rx_opt.dsack))
 		return -1;
 
···
 		return 0;
 
 	/* Do we need to wait to drain cwnd? With none in flight, don't stall */
-	if (tcp_packets_in_flight(tp) + 2 > tp->snd_cwnd) {
+	if (tcp_packets_in_flight(tp) + 2 > tcp_snd_cwnd(tp)) {
 		if (!tcp_packets_in_flight(tp))
 			return -1;
 		else
···
 	if (!tcp_transmit_skb(sk, nskb, 1, GFP_ATOMIC)) {
 		/* Decrement cwnd here because we are sending
 		 * effectively two packets. */
-		tp->snd_cwnd--;
+		tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) - 1);
 		tcp_event_new_data_sent(sk, nskb);
 
 		icsk->icsk_mtup.probe_size = tcp_mss_to_mtu(sk, nskb->len);
···
 	else
 		tcp_chrono_stop(sk, TCP_CHRONO_RWND_LIMITED);
 
-	is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tp->snd_cwnd);
+	is_cwnd_limited |= (tcp_packets_in_flight(tp) >= tcp_snd_cwnd(tp));
 	if (likely(sent_pkts || is_cwnd_limited))
 		tcp_cwnd_validate(sk, is_cwnd_limited);
 
···
 	if (unlikely(!skb)) {
 		WARN_ONCE(tp->packets_out,
 			  "invalid inflight: %u state %u cwnd %u mss %d\n",
-			  tp->packets_out, sk->sk_state, tp->snd_cwnd, mss);
+			  tp->packets_out, sk->sk_state, tcp_snd_cwnd(tp), mss);
 		inet_csk(sk)->icsk_pending = 0;
 		return;
 	}
···
 		if (!hole)
 			tp->retransmit_skb_hint = skb;
 
-		segs = tp->snd_cwnd - tcp_packets_in_flight(tp);
+		segs = tcp_snd_cwnd(tp) - tcp_packets_in_flight(tp);
 		if (segs <= 0)
 			break;
 		sacked = TCP_SKB_CB(skb)->sacked;

net/ipv4/tcp_rate.c

···
 	    /* Nothing in sending host's qdisc queues or NIC tx queue. */
 	    sk_wmem_alloc_get(sk) < SKB_TRUESIZE(1) &&
 	    /* We are not limited by CWND. */
-	    tcp_packets_in_flight(tp) < tp->snd_cwnd &&
+	    tcp_packets_in_flight(tp) < tcp_snd_cwnd(tp) &&
 	    /* All lost packets have been retransmitted. */
 	    tp->lost_out <= tp->retrans_out)
 		tp->app_limited =

net/ipv4/tcp_scalable.c

···
 		if (!acked)
 			return;
 	}
-	tcp_cong_avoid_ai(tp, min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT),
+	tcp_cong_avoid_ai(tp, min(tcp_snd_cwnd(tp), TCP_SCALABLE_AI_CNT),
 			  acked);
 }
 
···
 {
 	const struct tcp_sock *tp = tcp_sk(sk);
 
-	return max(tp->snd_cwnd - (tp->snd_cwnd>>TCP_SCALABLE_MD_SCALE), 2U);
+	return max(tcp_snd_cwnd(tp) - (tcp_snd_cwnd(tp)>>TCP_SCALABLE_MD_SCALE), 2U);
 }
 
 static struct tcp_congestion_ops tcp_scalable __read_mostly = {

net/ipv4/tcp_vegas.c

···
 
 static inline u32 tcp_vegas_ssthresh(struct tcp_sock *tp)
 {
-	return  min(tp->snd_ssthresh, tp->snd_cwnd);
+	return  min(tp->snd_ssthresh, tcp_snd_cwnd(tp));
 }
 
 static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 acked)
···
 			 * This is:
 			 *     (actual rate in segments) * baseRTT
 			 */
-			target_cwnd = (u64)tp->snd_cwnd * vegas->baseRTT;
+			target_cwnd = (u64)tcp_snd_cwnd(tp) * vegas->baseRTT;
 			do_div(target_cwnd, rtt);
 
 			/* Calculate the difference between the window we had,
 			 * and the window we would like to have. This quantity
 			 * is the "Diff" from the Arizona Vegas papers.
 			 */
-			diff = tp->snd_cwnd * (rtt-vegas->baseRTT) / vegas->baseRTT;
+			diff = tcp_snd_cwnd(tp) * (rtt-vegas->baseRTT) / vegas->baseRTT;
 
 			if (diff > gamma && tcp_in_slow_start(tp)) {
 				/* Going too fast. Time to slow down
···
 				 * truncation robs us of full link
 				 * utilization.
 				 */
-				tp->snd_cwnd = min(tp->snd_cwnd, (u32)target_cwnd+1);
+				tcp_snd_cwnd_set(tp, min(tcp_snd_cwnd(tp),
+							 (u32)target_cwnd + 1));
 				tp->snd_ssthresh = tcp_vegas_ssthresh(tp);
 
 			} else if (tcp_in_slow_start(tp)) {
···
 					/* The old window was too fast, so
 					 * we slow down.
 					 */
-					tp->snd_cwnd--;
+					tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) - 1);
 					tp->snd_ssthresh
 						= tcp_vegas_ssthresh(tp);
 				} else if (diff < alpha) {
 					/* We don't have enough extra packets
 					 * in the network, so speed up.
 					 */
-					tp->snd_cwnd++;
+					tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
 				} else {
 					/* Sending just as fast as we
 					 * should be.
···
 				}
 			}
 
-			if (tp->snd_cwnd < 2)
-				tp->snd_cwnd = 2;
-			else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
-				tp->snd_cwnd = tp->snd_cwnd_clamp;
+			if (tcp_snd_cwnd(tp) < 2)
+				tcp_snd_cwnd_set(tp, 2);
+			else if (tcp_snd_cwnd(tp) > tp->snd_cwnd_clamp)
+				tcp_snd_cwnd_set(tp, tp->snd_cwnd_clamp);
 
 			tp->snd_ssthresh = tcp_current_ssthresh(sk);
 		}

net/ipv4/tcp_veno.c

···
 
 		rtt = veno->minrtt;
 
-		target_cwnd = (u64)tp->snd_cwnd * veno->basertt;
+		target_cwnd = (u64)tcp_snd_cwnd(tp) * veno->basertt;
 		target_cwnd <<= V_PARAM_SHIFT;
 		do_div(target_cwnd, rtt);
 
-		veno->diff = (tp->snd_cwnd << V_PARAM_SHIFT) - target_cwnd;
+		veno->diff = (tcp_snd_cwnd(tp) << V_PARAM_SHIFT) - target_cwnd;
 
 		if (tcp_in_slow_start(tp)) {
 			/* Slow start. */
···
 			/* In the "non-congestive state", increase cwnd
 			 * every rtt.
 			 */
-			tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
+			tcp_cong_avoid_ai(tp, tcp_snd_cwnd(tp), acked);
 		} else {
 			/* In the "congestive state", increase cwnd
 			 * every other rtt.
 			 */
-			if (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
+			if (tp->snd_cwnd_cnt >= tcp_snd_cwnd(tp)) {
 				if (veno->inc &&
-				    tp->snd_cwnd < tp->snd_cwnd_clamp) {
-					tp->snd_cwnd++;
+				    tcp_snd_cwnd(tp) < tp->snd_cwnd_clamp) {
+					tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) + 1);
 					veno->inc = 0;
 				} else
 					veno->inc = 1;
···
 				tp->snd_cwnd_cnt += acked;
 		}
 done:
-		if (tp->snd_cwnd < 2)
-			tp->snd_cwnd = 2;
-		else if (tp->snd_cwnd > tp->snd_cwnd_clamp)
-			tp->snd_cwnd = tp->snd_cwnd_clamp;
+		if (tcp_snd_cwnd(tp) < 2)
+			tcp_snd_cwnd_set(tp, 2);
+		else if (tcp_snd_cwnd(tp) > tp->snd_cwnd_clamp)
+			tcp_snd_cwnd_set(tp, tp->snd_cwnd_clamp);
 	}
 	/* Wipe the slate clean for the next rtt. */
 	/* veno->cntrtt = 0; */
···
 
 	if (veno->diff < beta)
 		/* in "non-congestive state", cut cwnd by 1/5 */
-		return max(tp->snd_cwnd * 4 / 5, 2U);
+		return max(tcp_snd_cwnd(tp) * 4 / 5, 2U);
 	else
 		/* in "congestive state", cut cwnd by 1/2 */
-		return max(tp->snd_cwnd >> 1U, 2U);
+		return max(tcp_snd_cwnd(tp) >> 1U, 2U);
 }
 
 static struct tcp_congestion_ops tcp_veno __read_mostly = {

net/ipv4/tcp_westwood.c

···
 
 	switch (event) {
 	case CA_EVENT_COMPLETE_CWR:
-		tp->snd_cwnd = tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
+		tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);
+		tcp_snd_cwnd_set(tp, tp->snd_ssthresh);
 		break;
 	case CA_EVENT_LOSS:
 		tp->snd_ssthresh = tcp_westwood_bw_rttmin(sk);

net/ipv4/tcp_yeah.c

···
 
 	if (!yeah->doing_reno_now) {
 		/* Scalable */
-		tcp_cong_avoid_ai(tp, min(tp->snd_cwnd, TCP_SCALABLE_AI_CNT),
+		tcp_cong_avoid_ai(tp, min(tcp_snd_cwnd(tp), TCP_SCALABLE_AI_CNT),
 				  acked);
 	} else {
 		/* Reno */
-		tcp_cong_avoid_ai(tp, tp->snd_cwnd, acked);
+		tcp_cong_avoid_ai(tp, tcp_snd_cwnd(tp), acked);
 	}
 
 	/* The key players are v_vegas.beg_snd_una and v_beg_snd_nxt.
···
 			/* Compute excess number of packets above bandwidth
 			 * Avoid doing full 64 bit divide.
 			 */
-			bw = tp->snd_cwnd;
+			bw = tcp_snd_cwnd(tp);
 			bw *= rtt - yeah->vegas.baseRTT;
 			do_div(bw, rtt);
 			queue = bw;
···
 			if (queue > TCP_YEAH_ALPHA ||
 			    rtt - yeah->vegas.baseRTT > (yeah->vegas.baseRTT / TCP_YEAH_PHY)) {
 				if (queue > TCP_YEAH_ALPHA &&
-				    tp->snd_cwnd > yeah->reno_count) {
+				    tcp_snd_cwnd(tp) > yeah->reno_count) {
 					u32 reduction = min(queue / TCP_YEAH_GAMMA ,
-							    tp->snd_cwnd >> TCP_YEAH_EPSILON);
+							    tcp_snd_cwnd(tp) >> TCP_YEAH_EPSILON);
 
-					tp->snd_cwnd -= reduction;
+					tcp_snd_cwnd_set(tp, tcp_snd_cwnd(tp) - reduction);
 
-					tp->snd_cwnd = max(tp->snd_cwnd,
-							   yeah->reno_count);
+					tcp_snd_cwnd_set(tp, max(tcp_snd_cwnd(tp),
+								 yeah->reno_count));
 
-					tp->snd_ssthresh = tp->snd_cwnd;
+					tp->snd_ssthresh = tcp_snd_cwnd(tp);
 				}
 
 				if (yeah->reno_count <= 2)
-					yeah->reno_count = max(tp->snd_cwnd>>1, 2U);
+					yeah->reno_count = max(tcp_snd_cwnd(tp)>>1, 2U);
 				else
 					yeah->reno_count++;
 
···
 		 */
 		yeah->vegas.beg_snd_una  = yeah->vegas.beg_snd_nxt;
 		yeah->vegas.beg_snd_nxt  = tp->snd_nxt;
-		yeah->vegas.beg_snd_cwnd = tp->snd_cwnd;
+		yeah->vegas.beg_snd_cwnd = tcp_snd_cwnd(tp);
 
 		/* Wipe the slate clean for the next RTT. */
 		yeah->vegas.cntRTT = 0;
···
 	if (yeah->doing_reno_now < TCP_YEAH_RHO) {
 		reduction = yeah->lastQ;
 
-		reduction = min(reduction, max(tp->snd_cwnd>>1, 2U));
+		reduction = min(reduction, max(tcp_snd_cwnd(tp)>>1, 2U));
 
-		reduction = max(reduction, tp->snd_cwnd >> TCP_YEAH_DELTA);
+		reduction = max(reduction, tcp_snd_cwnd(tp) >> TCP_YEAH_DELTA);
 	} else
-		reduction = max(tp->snd_cwnd>>1, 2U);
+		reduction = max(tcp_snd_cwnd(tp)>>1, 2U);
 
 	yeah->fast_count = 0;
 	yeah->reno_count = max(yeah->reno_count>>1, 2U);
 
-	return max_t(int, tp->snd_cwnd - reduction, 2);
+	return max_t(int, tcp_snd_cwnd(tp) - reduction, 2);
 }
 
 static struct tcp_congestion_ops tcp_yeah __read_mostly = {

net/ipv6/tcp_ipv6.c

···
 		   jiffies_to_clock_t(icsk->icsk_rto),
 		   jiffies_to_clock_t(icsk->icsk_ack.ato),
 		   (icsk->icsk_ack.quick << 1) | inet_csk_in_pingpong_mode(sp),
-		   tp->snd_cwnd,
+		   tcp_snd_cwnd(tp),
 		   state == TCP_LISTEN ?
 			fastopenq->max_qlen :
 			(tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh)